(1) Field of the Invention
This invention comprises catalysts and a process to manufacture itaconic acid via condensation of succinic acid or its esters and formaldehyde. Components of the invention include the catalysts, which facilitate the condensation to form the intermediate citraconic anhydride, and the subsequent process steps for separation of citraconic anhydride from unreacted succinate, and conversion of citraconate to itaconate. The process facilitates the use of a number of formaldehyde and succinate substrates, and produces higher selectivity toward the desired products at lower cost than the prior art. Itaconic acid is a valuable monomer in the formulation of polymers because of its unique chemical properties, which derive primarily from the conjugation of its two carboxyl groups and its methylene group. The methylene group is able to take part in addition polymerization giving polymers with many free carboxyl groups that confer advantageous properties on the resulting polymer.
(2) Description of Related Art
Itaconic acid is currently produced commercially by the fermentation of glucose using Aspergillus Terreus. This fungal fermentation is carried out in batch processes, which require 8-10 days per batch. The fermentation requires dilute solutions (xcx9c10 wt % glucose as a feed) and itaconate yields are on the order of 50-60% of theoretical. The current world market for itaconic acid is approximately 20 million lb/yr at a selling price of $2.00/lb. The only U.S. manufacturer at present is Cargill (Minneapolis, Minn.).
The catalytic route to itaconic acid has several distinct advantages over the current commercial fungal fermentation route. First, the rate of the catalytic reaction is several orders of magnitude faster than the biological reaction, so that the reactor vessel is smaller than the fermenter. Second, the difficulties involved with the fungal fermentation (product inhibition, sensitivity of microorganisms to process changes, etc.) are avoided. Third, separation and recovery costs should be lower via the catalytic route, so the expected production cost of itaconic acid is substantially lower than via fermentation.
There exist several patents in the literature which describe catalytic routes to citraconate or itaconate from succinates. U.S. Pat. No. 3,835,162 (Tate and Berg, assigned to Pfizer, Inc., 1974) describes catalysts and process conditions for reactions of succinic anhydride or succinate esters and formaldehyde (as trioxane or gaseous formaldehyde, in 3 to 5-fold excess) to citraconic anhydride. Yields as high as 70% were obtained for short periods of time in a microreactor consisting of a gas chromatography column packed with catalyst. The catalyst consisted of salts (thorium sulfate, potassium hydrogen phosphate, lithium phosphate, and others) supported on a lower surface area alumina (30-40 m2/g); catalyst deactivation was observed at extended reaction times. A crude method for recovery of itaconate was described.
Another prior process for producing itaconate from succinate is described in two Japanese patents (JP 49101326 and JP 49101327, Shimizui and Fujii, assigned to Denki Kagaku Kogyo K. K., 1974). Silica-alumina compounds, including zeolitic materials, both with and without the addition of salts such as copper chloride, zinc chloride, or lanthanum chloride, were used as catalysts. In all studies, formaldehyde (as Formalin or trioxane) was used as the limiting reagent. Yields of citraconate plus itaconate up to 75% of theoretical based on formaldehyde were obtained, but yields based on succinate fed were no greater than 32%. These patents gave no information regarding a process for the conversion to itaconate, and there is no mention of the problem of catalyst deactivation or recycling of the succinate stream.
Sakai (Bull. Chem. Soc. Japan 49 219 (1976)) has further investigated the isomerization of citraconic acid to itaconic acid, and achieved yields of 65% itaconic acid. Sakai makes no mention of a recycle step or the reisomerization of byproducts back to citraconic acid. The conversion of citramalic acid, one of the byproducts of citraconic acid isomerization, back to citraconic acid has been reported by Berg (U.S. Pat. No. 3,960,901 to Pfizer (1976)).
The present invention relates to a process for the preparation of citraconic anhydride which comprises: contacting a molar excess of an aqueous solution of formaldehyde, gaseous formaldehyde or trioxane in a solvent with at least one compound from the group consisting of succinic anhydride and di-lower alkyl esters of succinic acid in vapor phase at a temperature from about 320xc2x0 to 440xc2x0 C., at a pressure from about 20 to 400 psi, at a Weight Hourly Space Velocity (WHSV) from about 0.3 to 4 kg succinate/hr*kg catalyst in the presence of a catalyst consisting of a porous material having a surface area between about 30 m2/g and 700 m2/g, surface acid site density from about 66 to 2350 micromole/g, surface base site density from about 0 to 500 micromole/g and acid strength (pKa) of about +3 to xe2x88x923 until reaction is substantially complete and recovering from the reaction products the citraconic anhydride thereby produced, said lower alkyl having from 1 to 4 carbon atoms. The citraconic anhydride is hydrolyzed and isomerized to itaconic acid in an aqueous solution.
The present invention particularly relates to a process for the preparation of itaconic acid from citraconic acid which comprises:
(a) isomerizing citraconic acid to itaconic acid in an aqueous solution at a first temperature of about 140xc2x0 C. to 200xc2x0 C., which produces citramalic acid and mesaconic acid as by-products;
(b) crystallizing and separating the itaconic acid from the aqueous solution by cooling to a temperature between about 20xc2x0 to 25xc2x0 C.; and
(c) heating the aqueous solution from step (b) to a temperature of 200xc2x0 to 300xc2x0 C. in the presence of a catalyst to convert any of the itaconic acid remaining in the aqueous solution and the by-products in the aqueous solution to citraconic acid;
(d) recycling the citraconic acid solution of step (c) to step (a).
The present invention is superior to that of the Pfizer patent (U.S. Pat. No. 3,835,162) in several ways. First, it requires only a metal oxide such as alumina in order to obtain good yields. This catalyst is more stable than the salt-impregnated alumina described in the Pfizer patent, especially during the catalyst regeneration step (an integral part of the process). Second, it has been demonstrated that Formalin(trademark) (37% formaldehyde in water) and Formcel(trademark) (55% formaldehyde in methanol/water) can be used instead of trioxane or gaseous formaldehyde. Both of these alternate formaldehyde sources are readily available commercially, whereas trioxane or gaseous formaldehyde are not. Third, the present invention includes an improved process for forming and purifying itaconic acid. Finally, it is has been demonstrated by this invention that a continuous flow reaction system is much closer to a commercially viable process concept than the micro-reactor system used in the Pfizer patent.
The present invention provides a more complete process for converting succinate to itaconate than the Japanese patents, including a succinate recycle step, catalyst regeneration, and recovery and purification of itaconic acid. Formcel is a viable formaldehyde source in addition to Formalin. The porous material catalyst is generally aluminum based and has particular characteristics as defined above. It has a mildly acidic and basic surface.
The present invention also relates to a process for the preparation of formaldehyde, citraconic acid and succinic acid which comprises:
(a) reacting a molar excess of formaldehyde with dimethyl succinate in vapor phase with a catalyst, the catalyst consisting of a porous material having a surface area between about 30 m2/g and 700 m2/g, surface acid site density from about 66 to 2350 micromole/g, surface base site density from about 0 to 500 micromole/g and acid strength (pKa) of about +3 to xe2x88x923 until reaction is substantially complete and recovering from the reaction products the citraconic anhydride thereby produced, said lower alkyl having from 1 to 4 carbon atoms at a temperature of 320xc2x0 to 440xc2x0 C. at a pressure of about 20 to 400 psi;
(b) hydrolyzing the citraconic anhydride to citraconic acid and the dimethyl succinate to succinic acid at elevated temperatures in water so that the methanol is distilled from the reaction mixture;
(c) oxidizing the methanol from step (b) to produce formaldehyde; and
(d) separating the citraconic acid and succinic acid from the reaction mixture.
In summary, the present invention is a new route for itaconic acid formation from succinates. It encompasses a complete process for the conversion which includes catalysts and reaction conditions for efficient conversion.
The present invention uses preferred alumina based solid particles which are substantially free of other metals. The particles are calcined and have an acid strength pKa between about xe2x88x923 and 3 and a surface area of at least about 100 m2/g. Included in the preferred materials are gamma alumina and calcined aluminum phosphate. Gamma alumina is described in U.S. Pat. No. 6,015,485 to Shukis et al; U.S. Pat. No. 5,166,121 to Khare et al; U.S. Pat. No. 5,032,379 to Pedersen; U.S. Pat. No. 4,301,033 to Takumi et al; U.S. Pat. No. 4,235,756 to Slauqh; U.S. Pat. No. 4016,106 to Sawyer et al; U.S. Pat. No. 3,835,162 to Tate et al.